The mechanistic interpretation of RPV high Ni materials data radiation damage is an important scientific issues and a key element in view of proper embrittlement forecasting and mitigation. The temperature transition shifts due to irradiation observed for the available sets of material data, surveillance data of WWER-1000 RPVs in particular, are showing, in spite of scatter in the data, consistent behaviour and give indication that Mn as well as Ni are playing a key role in embrittlement together with Cu and P and other impurities. Evidences of synergisms are also appearing examining sub-sets of data or behaviour of model alloys. However, the embrittlement kinetics of high Ni-Mn steels is not fully understood; in particular the mechanistic explanation of the observed behaviour.
This could be of primary importance for the prediction and forecast of WWER and PWR RPVs embrittlement and for correct understanding and use of the available related surveillance data. For WWER, at present a dedicated Tacis TAREG project is being launched in order to re-evaluated further and produce complementary data and to provide a better d-base for further modelling work. Based on available surveillance data, examined statistically in the last few years, some preliminary conclusions, as well as a key to forecast, can be drawn based on the mechanistic interpretation given in this paper.
The main conclusions are that increasing levels of Ni and Mn contents are gradually accelerating precipitation and segregation processes while affecting rather marginally basic matrix damage. This fact is of fundamental importance because it allows optimistic forecast of long term radiation damage for those observed cases where, in combination with high Ni and high Mn contents, the surveillance data show unexpected high DBTT shifts.